The invention relates to repairing or replacing a bimetallic weld in a jet pump diffuser assembly and, more particularly, to a jet pump diffuser clamping assembly that structurally replaces/repairs the weld.
In a boiling water nuclear reactor, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core flow. The lower portion of the jet pump is a long conical tubular section. The function of the diffuser is to slow the high velocity flow stream and thus convert the dynamic head of the flow stream into static pressure.
The jet pump diffuser assemblies in boiling water reactors can be one of two differing design configurations. The first configuration incorporates an adapter component, which is comprised of an upper austenitic stainless steel ring and a lower inconel alloy 600 ring. These two rings were shop-welded, as this was a bimetallic weld (a weld of dissimilar metals) and more difficult to perform than a weld joining similar metals. This adapter component then facilitated the assembly of the diffuser in the reactor, as the lower section of the adapter was welded to the inconel alloy 600 shroud support plate. The diffuser tail pipe being constructed of austenitic stainless steel was then joined to the upper section of the adapter, which was constructed of austenitic stainless steel. As such, at the time of field construction of the reactor these two welds of similar metals were performed.
The second design configuration consists of a lower ring constructed of inconel alloy 600, shop-welded to the diffuser tail pipe. Since the diffuser tail pipe is fabricated from austenitic stainless steel, this was a bimetallic weld. This design approach results in the welding of the lower ring to the shroud support plate as the only weld required to be performed at the time of field construction of the reactor.
Regardless of diffuser assembly design configuration under consideration, a bimetallic weld is present in the diffuser assembly. In the event that the structural integrity of the bimetallic weld of the diffuser assembly should become degraded, a means of reinforcing or structurally replacing this weld is desired.